1. Field of the Invention
The present invention relates to a motor control apparatus for controlling a motor which is mounted in a hybrid vehicle.
This application is based on Japanese Patent Application, Unpublished, No. Hei 11-291699, the contents of which are incorporated herein by reference.
2. Description of the Related Art
There are known hybrid vehicles, each of which has a motor in addition to an engine as a power source for driving the vehicle. Hybrid vehicles are classified into series hybrid vehicles and parallel hybrid vehicles.
In a series hybrid vehicle, the motor is driven by power output or the like from a generator which is driven by an engine, and the wheels are driven by means of the motor. As the engine is not mechanically coupled to the wheels in the series hybrid vehicle, the engine can run at approximately a constant speed in a speed range with high fuel consumption rate and low emissions, thus ensuring higher fuel consumption rate and lower emissions than conventional engine vehicles.
By contrast, a parallel hybrid vehicle uses a motor coupled to an engine to assist driving of the drive shaft of the engine and has a power storage unit which is charged by electric energy that is acquired by using this motor as a generator. This generated electric energy is also used by electrical equipment in the vehicle. A parallel hybrid vehicle can therefore reduce the operational load of the engine and can also ensure a higher fuel consumption rate and lower emission than a conventional engine vehicle.
There are several types of parallel hybrid vehicles. In one type of parallel hybrid vehicle, the motor is directly coupled to the output shaft of the engine to assist the engine output and serves as a generator at the time of deceleration, generating electric energy which is stored in a battery or the like. In another type of parallel hybrid vehicle, either one of the engine and the motor or both can generate driving force and a generator is provided separately.
Such hybrid vehicles are designed to execute various operations, such as assisting the engine output by using the motor, for example, at the time of acceleration and charging the battery or the like by deceleration regeneration at the time of deceleration, to thereby secure electric energy of the battery. The secured electric energy can allow the hybrid vehicles to meet with drivers"" demands.
The motor that is used in a hybrid vehicle assists the engine output and performs deceleration regeneration in accordance with the running conditions of the vehicle. The output control for such operations is often accomplished by feedback control on demanded power or demanded current.
If some sort of abnormality occurs in the control loop that executes feedback control, however, the feedback control is carried out based on this abnormal output value. This may lead to a change in the behavior of the vehicle that does not meet a driver""s demand.
Accordingly, it is an object of the present invention to provide a motor control apparatus for a hybrid vehicle, which can detect an abnormality in the control loop and can suppress a change in the behavior of the vehicle that does not meet a driver""s demand when the abnormality occurs.
In the first aspect of the present invention, a motor control apparatus (for example, a motor control apparatus 5 in the embodiment) for a hybrid vehicle with an engine (an engine 1) for outputting driving force of the vehicle, a motor (a motor 2) for generating driving force for assisting the output from the engine and a battery (a battery 3) for supplying power to the motor and for storing electric energy regenerated by the motor acting as a generator when the driving force is not required, comprising: a detector (a sensor 12, current sensors 13,15 and 17, voltage sensors 14 and 16) for detecting supplied power to the motor or supplied current to the motor; a feedback controller (a demanded power computing section 51, a real power computing section 52, and a feedback control section 53) for performing feedback control to keep the supplied power or the supplied current at a target value based on the detection result from the detector; an abnormality detector (an abnormality detecting section 54) for detecting an abnormality in the detector; and an abnormality processing device (an abnormality processing section 55) for fixing supplied power or supplied current to the motor to a predetermined value by reducing a gain in the feedback control or stopping the feedback control until a predetermined time elapses since detection of an abnormality in the detector, and stopping controlling the motor after the predetermined time elapses since detection of the abnormality.
The structure according to the first aspect of the present invention does not permit feedback control to be executed based on a feedback control loop where an abnormality has occurred, and can thus prevent the occurrence of a change in the behavior of the vehicle that does not meet a driver""s demand.
In the second aspect of the present invention, the abnormality processing device restricts a speed of the engine in such a way that a counter electromotive force generated by the motor when control on the motor is stopped does not exceed a predetermined value (step S8).
The structure according to the second aspect of the present invention limits the engine speed in such a way that when motor control is stopped, the counter electromotive force generated by the motor does not exceed a predetermined value. This provides an advantage of preventing the counter electromotive force generated by the motor coupled to the engine from going high and over the allowable voltage for a power drive unit or the like.
In the third aspect of the present invention, the detector includes sensors (current sensors 15 and 17, voltage sensors 14 and 16), provided on both battery and motor sides, for detecting the supplied power or the supplied current; and the abnormality detector detects the abnormality based on a difference between output values of the sensors.
The structure according to the third aspect of the present invention compares the output values of a plurality of sensors with one another so as to be able to detect such a phenomenon that the output value of one sensor is fixed to a certain value although it is not higher than the upper limit or lower than the lower limit.